Radius worktop with edges squared off

Hi All
Im trying to get a worktop which effectively has 480mm radius corners onto the worktops adjacent to it which are 600mm and 500mm but need to square the worktop off to butt up to the other worktops. The curved top is 40mm and the worktops are 30mm. I can round off edges etc but cant cut the straight edges across. Also its above a curved panel and unless I remove the curved panel everytime I try and edit it it moves down the page, and I cant move it back without coming out of editing and then the frustrating circle happens again.
Help!!!!!

Just making it for you in TurboCAD

What profile do you want on the top?
The Panelling below, are you wanting this to look like individual T&G boards (faceted to board width) or a smooth curve?

Hi Darrel
Just a small pencil round would be great including the edges where it sits above the stone. 
Many Thnaks

Forgot to say. The panel underneath I have created already. Why does the custom worktop keep moving when going into edit? 
Also the nib on the wall is 150mm x 90mm.
I drew this kitchen in Vectorworks CAD creating a dwg. drawing is there a way I could of taken it from that?

If the Vectorworks drawing was 3D then yes if it's easy to save it out as a skp file or something Sketchup can open...

See attached (Worktop Only)… hope this helps...

Thanks Darrel.